(1) Field of the Invention
The present invention relates to a method of managing discontinuities in the control of a vehicle following a control transition, and also to a vehicle applying the method.
The invention lies more particularly in the field of piloting relationships and more particularly of devices for managing control discontinuities as a result of changing piloting relationships, or of making a change within a single relationship. The invention is particularly advantageous for electrical or optical flight control systems with piloting members having a neutral centered position.
The present invention thus lies in particular in the technical field of electrical or optical controls for controlling the movement of a vehicle, and in particular electrical or optical flight controls for an aircraft.
(2) Description of Related Art
An aircraft usually has control members that can be controlled in order to control the aircraft. The control members may for example comprise airfoil surfaces or indeed members that expel a fluid from the aircraft.
In this context, a rotorcraft has a main rotor that provides the rotorcraft with propulsion and with lift. The pitch of the blades of the main rotor can be adjusted in cyclic or collective manner in order to control the movement of the aircraft in three-dimensional space.
Furthermore, a rotorcraft may have a control member referred to for convenience as an “auxiliary” member for controlling the yaw movement of the rotorcraft. By way of example, such an auxiliary member may either be a tail rotor or else a device that expels fluid sideways.
In order to control such control members, the aircraft may have controls that can be operated by a pilot, where such a control is referred to for convenience as a “pilot control”.
Pilot controls are connected in mechanical and/or non-mechanical manner to actuators that move the control members. Non-mechanical pilot controls may comprise electrical or optical controls.
In the context of non-mechanical control, a pilot control may generate a signal that is transmitted to a processor system. Such a processor system may for example comprise a processor unit referred to as a primary flight control system. This processor system then responds to said signal by generating an order with the help of a piloting relationship, the order serving to control at least one actuator that acts directly or indirectly on at least one control member. Such a pilot control may be referred to more simply as an “electrical or optical control”.
An electrical or optical control may comprise a joystick, a lever, pedals, . . . .
The electrical or optical signal transmitted by an electrical or optical control may represent the spatial position of the electrical or optical control. The processor unit then inputs this position into a piloting relationship in order to determine the orders to be transmitted to one or more actuators.
Furthermore, an electrical or optical control does not necessarily control a parameter of a control device, such as the pitch of the blades of the main rotor, for example. The electrical or optical control may define a target to be reached by operating the various control members. For example, the electrical or optical control may be operated to specify a speed setpoint to be reached by the aircraft, with the processor system then generating the orders for transmission to the control members in order to reach the setpoint speed.
Thus, the processor unit uses a piloting relationship to generate an order that can be said to be “indirect” insofar as the order is not transmitted directly to an actuator. The indirect order is transmitted to a piloting unit that then generates an order that can be referred to as “direct”, the direct order then being transmitted to at least one actuator.
For reasons of vehicle operability, the processor unit may include a plurality of different piloting relationships. The piloting relationships may change, in particular as a function of the stage of flight, or indeed as a function of a piloting mode, e.g. as selected by a pilot.
For example, the processor unit may act during a stage of low speed flight to apply a piloting relationship that generates an indirect order specifying a longitudinal ground speed to be reached. In contrast, during a stage of high speed flight, the processor unit may apply a piloting relationship that generates an indirect order specifying an indicated air speed to be reached.
The transition from one piloting relationship to another piloting relationship can then give rise to discontinuity in control.
Specifically, switching between two piloting relationships may take place automatically in order to reduce the workload on the crew. Furthermore, two distinct relationships do not necessarily produce the same setpoint for the actuators for a given position of an electrical control.
Consequently, a pilot may position an electrical or optical control in a given position. In this position a first piloting relationship generates at least one first order that is transmitted to at least one control member. Unfortunately, the two relationships do not necessarily produce the same order for the same position of the electrical or optical control.
Thus, when the electrical control is in this given position, the second relationship may generate at least one second order that is different from the first order. A sudden switch from the first relationship to the second relationship can then produce a jolt on the control that is referred to as a “control discontinuity”, or more simply as a “discontinuity”. This discontinuity is harmful not only for the path followed by the vehicle, but also for the comfort of the crew and passengers, if any, and indeed for the mechanical strength of the controlled control members.
Switching between two piloting relationships is not the only source of discontinuity. Certain pilot actions can also give rise to discontinuities.
For example, a joystick may be moved about a neutral position in which the joystick gives a reference order. A pilot has the option of modifying this reference order. Thus, the pilot may move the joystick into a deflected position representing a desired new reference order. Then using a selector knob, the pilot can specify that the order being transmitted by the joystick corresponds henceforth to the reference order to be supplied when the joystick is in its neutral position.
However, the joystick is still in its deflected position, and that leads to a discontinuity.
To solve that problem, instead of performing the operation of modifying the reference of the joystick by tilting the joystick, it can be performed by using an interface that is dedicated to that operation. The pilot then modifies the reference order with the help of the interface while keeping the joystick in the neutral position in order to avoid a discontinuity.
The problem of discontinuities also covers transitions between different computers in a given architecture, e.g. in the result of a failure, or indeed transitions between two distinct piloting modes, e.g. in the event of a failure of a primary sensor.
Below, the term “control transition” is used to refer to a transition between two piloting relationships, or indeed to a transition between two references of a pilot control. Consequently, a control transition is any transition that might generate a discontinuity in the controls of a vehicle.
Several solutions exist for limiting the impact of a control discontinuity.
A first solution consists in spreading out the passage from one piloting relationship to another piloting relationship, e.g. by limiting the speed of execution of an order generated by the piloting relationship. This limitation does indeed serve to limit the effect of a discontinuity.
In the above example, passing from the first order that results from applying a first piloting relationship to a second order that results by way of example from applying a second piloting relationship takes place progressively at a speed that is limited. That first solution serves to reduce jolts that result from the discontinuity by slowing down the transition between two successive control orders that are different.
Nevertheless, that first solution tends to limit the speed of execution for any orders that are given, even in the absence of a discontinuity. The person skilled in the art thus needs to find a compromise between the dynamic behavior of the piloting relationship and the hardness of the jolt that is suffered as a result of switching between two piloting relationships.
If the person skilled in the art seeks to have discontinuities that are very well smoothed, then speed limitations are set to match control speeds that are very slow, thereby penalizing the responsiveness of the piloting relationship. Conversely, if the responsiveness of the piloting relationship is preferred, then the speed limitations are adjusted to control speeds that are fast, thereby limiting the effect of discontinuity smoothing.
A second solution consists in using a software component referred to as a “fader”.
Unlike the first solution, this component applies a speed limitation only on a difference between orders coming from two different piloting relationships at the time of switching between those two piloting relationships.
The second solution makes it possible to avoid one of the drawbacks of the first solution. Specifically, in the absence of switching, the second solution does not act at all on the piloting relationship that is being implemented.
Like the first solution, the second solution makes it possible to spread out the switchover between two piloting relationships. If the spreading time is short, then the switchover can generate a jolt in the control. In contrast, if the time is too long, then control over the aircraft can be degraded.
A third solution consists in establishing a transition piloting relationship over a transition range. For example, in a speed range, a transition piloting relationship results from linear interpolation between two piloting relationships as a function of a speed of the aircraft.
Throughout the transition range, the pilot is nevertheless without control over a real physical magnitude. Pilotability in the transition relationship is thus degraded. In order to minimize that drawback, the transition range is minimized, thereby correspondingly limiting the benefits expected from such a method.
A fourth solution consists in causing two different relationships to converge on similar control orders in order to limit the control discontinuity, and thus limit its impact on board the vehicle. Although effective, the behavior of the aircraft at the time of transition can be difficult to assess.
The technological background includes the following documents: U.S. Pat. Nos. 8,729,848; 5,197,697; 8,050,780; and 8,725,321.
Document U.S. Pat. No. 8,729,848 describes a joystick co-operating with a passive force feedback system.
Document U.S. Pat. No. 5,197,697 describes a system enabling a pilot to operate a control in order to modify a control order of an autopilot system.
Document U.S. Pat. No. 8,050,780 describes a force feedback system for a control stick. A position signal and a force signal are used in a force feedback loop in order to control a motor that is mechanically connected to the stick.
Document U.S. Pat. No. 8,725,321 describes a pilot control that is mechanically connected to a segment of a control member. Furthermore, a force sensor measures the force exerted by a pilot on the pilot control. The force sensor sends a force signal to a processor unit that controls an actuator connected to another segment of the control member specifically as a function of said force signal.
Documents EP 0 718 731, US 2013/261853, and US 2007/164167 are also known.
Document EP 0 718 731 describes a device for actuating a controlled member of an aircraft. That device includes a computer connected to actuator means suitable for actuating a controlled member as a function of the action of a pilot on a control member.